The present invention relates generally to a strain-relief bushing for cables and the like, and more particularly to such a bushing which is intended to be installed in a hole formed in a wall of a casing, housing or the like so that the cable can lead from the exterior to the interior of the housing, or vice versa.
Strain-relief bushings for this purpose are already known. Their purpose is that which has been briefly outlined above, and they have the additional function for relieving strain, i.e., of preventing damage to the cable or the equipment with which it is connected in the interior of the housing. In most instances prior-art bushings utilize a plug of rubber or synthetic plastic which the cable (the term hereafter intended to refer not only to cables per se but also to wires and similar conductors) is pushed and which are then squeezed against the cable compressing them via a threaded element. However, it has been found that this does not provide any significant strain-relief and, further does not meet electrical codes which exist in some countries.
Another prior-art approach utilizes a bushing having a plurality of double-conical clamping jaws of synthetic plastic material which are pressed against one another and against a cable by means of a threaded element. The strain-relief afforded by this arrangement is adequate but the arrangement is relatively complicated and it is composed of a plurality of individual elements which must not only be individually produced but which then cause problems in assembly, making the use of this arrangement quite labor-intensive. However, even this arrangement does not meet certain electrical codes.
Another prior-art construction is a bracket which extends across the cable and is screwed down at opposite lateral sides of the cable, being pulled against the latter in order to hold it in place and provide a strain-relief. It also requires a plurality of components and is labor-extensive in terms of the labor required to assemble the arrangement. Furthermore, this arrangement also does not meet the electrical codes of some countries.
In all prior-art arrangements clamping devices are used the vector of whose clamping pressure extends at right angles to the longitudinal axis of the cable. This means that if sufficient clamping force is exerted, the cable is bent to a U-shaped configuration where it is engaged, and if an axial force then is exerted upon the cable this will result in damage to the same. Such damage is frequently observed when these prior-art devices are used, and defects in the cable installation can be very dangerous.